Apparatus and method for obtaining representative samples of the fluids produced by an oil well, and measuring the amounts of oil, water and gas in the sample.
The need for accurate and timely oil well production data is critical. The extremely erosive and harsh environments in which well pumping systems operate create constant deterioration of the equipment, often resulting in rapid failure. To maintain production rates in the face of this situation, well operators invest substantial resources in well maintenance. For wells using steam drives and waterfloods, well servicing is frequently the highest non-energy cost.
Knowledge of the production performance of an individual well on a current basis is the most important tool for maximizing production from the well and optimizing reservoir management. Because of the well-known advantages of prompt, accurate and low-cost performance data, numerous testing systems have been devised. Despite extensive previous efforts, there still remain many unsolved disadvantages, resulting in uncertainly of accuracy of the data, and long testing periods because the sampling procedures were very slow themselves.
Early pioneers in production of oil from wells as early as about 1900 began to measure the performance of their individual wells. The early efforts were little more than collecting well production for a day or so, and measuring the gross output and the relative amounts of water and oil with a dip stick or tape measure. That method is still widely used, but is not truly sufficient when optimum and most economical production is the objective.
Open tank systems can indeed accurately measure the output of low production rate wells, but they take a very long time to collect the sample. Worse, production conditions can vary widely during that long period. A true production sample representative of a short preselected period of time can not be obtained with this practice.
Beginning in the 1960""s this procedure was improved by providing tall, vertical, closed separators and using various mechanical devices to measure the levels and read them out. These largely succeeded because of the advent of pollution control rules, which adversely affected the earlier open tank samplers rather than because of any inherent sampling superiority. The closed samplers simply produced less pollution.
Beginning in the 1980""s improved sensing devices became available, and their use improved the accuracy of the procedures but still their collection times were slow, and they did not provide for suitable purging between tests, leading to contaminated samples. Also the potential for measurement errors in low flow rate wells was and is much higher than it should be. Additional problems reside in the complexity and inaccuracies of the more modern sensors and measuring devices, especially at slow flow rates. Because of their sophistication, the initial costs and the costs of maintenance and operation of these newer systems are much higher than they should be.
Especially in periods of low oil prices at the well, it is essential not only to minimize operation and maintenance costs, but also to maximize production both of the well and of its field. Dollars are very scarce in times of low oil prices, and any reduction of costs is not only welcomed but may contribute to the decision to keep a well or field in operation rather than to shut it down.
It is an object of this invention to provide sampling apparatus and method that can obtain a sample which is suitably small to reflect fluid produced in a relatively short time, even from low production rate wells. A single sampler has the capability to service a substantial number of wells, often up to 60 wells, and to provide frequent samples from them. Importantly, the lines leading to it are fully purged of fluid remaining from previous tests as is the apparatus itself so that the sample is truly representative of well production at a very specific time.
This apparatus can be operated manually. In practice, programs to cause the sequential operation of the valves will be provided. Such programs form no necessary part of the invention, and can readily be devised by persons skilled in the controls art.
This apparatus can be automated to perform its method on a programmed basis without supervision, and can also be programmed to alert the owner to any departure of a well""s performance from previous samplings, thereby alerting the operator to potential problems in a particular well.
It is an object of this invention to provide with minimal effort a clear and receptive tester for sequential tests for individual of a group of wells, and to provide a simplified arrangement to determine gas proportions.
In addition wells whose gas/oil ratio is very high involve special problems in measuring the gas of the product, which it is one object of this invention to overcome.
Sampling apparatus according to this invention includes a vessel having a bottom wall, a top wall and a vertically extending sidewall which form a sample chamber.
A water inlet passes through the bottom wall. A test fluid exit port passes through the top wall. A test fluid line opens into the vessel at a mid-elevation. A test fluid inlet valve controls flow from a test fluid supply line to the test fluid line. A purge line opens into the vessel at a lower elevation.
A sample exit sensor senses flow from the sample exit port, and a purge control valve controls flow from the purge line.
A return line returns fluid from the vessel to a point of use. A flow line interconnects the purge line and the sample exit line at their intersection downstream from their respective valves. A selector valve is placed between said intersection and the fluid exit valve.
A gas discharge line is connected between said fluid exit line and said return line. A gas control valve and a gas flow meter are placed in the gas discharge line.
A flow meter device is placed in said return line.
A test fluid by-pass line interconnects the test fluid supply line to the return line. A by pass valve selectively controls flow through the test fluid inlet line and through the return line.
By suitable manipulation of the aforesaid valves along with the availability of lease water under pressure, test fluid under well pressure, and a suitable return to the system, a unique sampling process can be accomplished.
This system utilizes water from a separate water supply often called xe2x80x9clease waterxe2x80x9d. This water is used and discarded as part of the procedure. This is not water from the samples.
A procedure according to this invention begins with the vessel full of water. First, the contents of the lines leading to the vessel wherever they may have come from will be forced into the vessel for a measured period of time. The pressure is that of the well production fluid. The water expelled by this incoming fluid passes through the flow meter. From this is calculated how long a time it will take for the flow from this well to completely form a suitable sample, or how large the sample will be in a selected period of time. This places produced material in the chamber.
The vessel next is closed and its contents permitted to settle (gas on top, water on the bottom, oil in between). During this time, test fluid from the well continues to purge the supply line through the by-pass.
Next gas is measured and purged. The lease water drives the fluids upwardly until liquid is sensed at a sensor (the supply line purge continuing). The gas flow through the gas flow meter measuring the gas content.
Oil is next purged from the vessel by further supply of lease water thereby driving oil out through the exit port. This driving action will continue until water has been sensed at the sensor for a given length of time, usually one minute. Thus, all of the piping downstream of the vessel will be purged.
Now a production sample is collected by opening the sample inlet valve and the water exit valve. The sample fluid will drive the purge water from the vessel and occupy the vessel by a known amount. After that time the vessel is closed and the sample water, gas and oil separate.
If desired for high oil/gas samples, a gas vent line is provided which relieves the vessel from excessive amounts of gas to enable a sufficient sample of oil to be obtained.
The above and other features of this invention will be fully understood from the following detailed description and the accompanying drawings, in which: